This invention relates to ink drop printing method and apparatus wherein continuous streams of drops are generated from liquid emitted under pressure through a nozzle. Selected drops are electrostatically charged and deflected between flight paths intersecting either a target to be printed or a drop collection gutter. More specifically, this invention relates to method and apparatus for reducing the amount of electrical connections necessary for charging ink drops in binary printers having high numbers of nozzles.
As used herein, a binary printer is one wherein each nozzle supplies ink drops to cover a single point or pixel in a scan line of a raster pattern used to form an image on a target. An individual drop either goes to the pixel associated with its nozzle or a gutter. Typically, a print drop is charged to a print level to reach the target and is charged to a gutter level to intercept the gutter. For example, a zero charge level may be the print level and some positive charge level of a significant non-zero magnitude may be the gutter level or vice versa.
A multiple nozzle binary printer places a burden on the complexity of the wiring and electronic circuitry needed to electrically address a high number of nozzles. For example, a rectangular raster pattern made up of scan lines having 3000 pixels or points requires a binary ink drop printer to have 3000 nozzles to cover each of the pixels. Each nozzle must be electrically addressed to set a drop to either of the binary charge levels: a print level or a gutter level. Conventionally, this requires that 3000 electrical connections be made to charging electrodes associated with each nozzle. Compounding the difficulty and complexity of such binary printers is that the nozzles are packed at a density of from about 20 to about 200 nozzles per centimeter (cm).